The adult cerebral cortex is capable of undergoing experience dependent functional changes. Such changes play a role in perceptual learning and recovery of function following CNS damage. The circuitry mediating adult cortical plasticity includes the plexus of long range horizontal connections formed by cortical pyramidal cells as well as the connections formed by inhibitory interneurons. The experience dependent changes in this circuitry involve the sprouting of new axonal connections and the pruning of preexisting connections. The proposed project involves investigating the molecular basis for the remodeling of axonal arbors, including signaling by neurotrophins and the caspase dependent apoptotic pathway. Using a mouse model of adult cortical plasticity involving remapping of the somatosensory cortex following whisker plucking and 2- photon in vivo longitudinal imaging of cortical axons, the role of different components in these signaling pathways in the process of axonal pruning and outgrowth will be determined. The experiments are designed to map the steps and molecular interactions leading from alterations in the patterns of neural activity to alterations in cortical circuits.